Effect of plasma membranes on solute transport in 3T3 cells

2,4-Dichlorophenoxyacetic acid influx is mediated by an active transport system in Chinese hamster ovary cells

The influx of 2,4-dichlorophenoxyacetic acid (2,4-D) into Chinese hamster ovary (CHO) cells was studied. The cells mainly took up but did not metabolize the undissociated form of the herbicide. The uptake of 2,4-D was carried out against a concentration gradient and was inhibited by sodium azide and dinitrophenol. The results presented here show that the herbicide influx was an active, energy dependent process. (Na+ + K+)ATPase does not seem to be involved because ouabain, an inhibitor of the enzyme, did not affect the 2,4-D uptake.

Density-dependent regulation of amino acid transport in a Burkitt lymphoma cell line

Rate of proliferation and amino acid transport were assessed in the Burkitt's lymphoma-derived Namalwa cells by measurements of growth rate and proline and serine uptake. Cell density of the cultures was varied by modifying the number of cells initially seeded and growing for different periods of time. Under these experimental conditions the growth rate was not correlated with cell density. In contrast, the activity of amino acid transport through Systems A and ASC, as assessed by the uptake of proline and serine, respectively, decreased as a function of cell density. This marked decrease of transport activity cannot be explained by large alterations of cell morphology since it was observed at a cell density range where minimal change of cell volume and surface area occurred. When a constant number of cells suspended in an identical volume of medium sedimented on different settling areas, a marked effect on amino acid transport activity occurred. These results indicate that cell to cell contacts may be involved in the density-dependent regulation of transport.

Dexamethasone and sphingolipids inhibit concanavalin A stimulated glucose uptake in 3T3-L1 fibroblasts

Studies were carried out in 3T3-L1 fibroblasts to determine the effect of sphingolipids and corticosteroids on concanavalin A stimulated glucose uptake. Sphinganine (40 microM) and sphingosine (40 AND 100 microM) significantly inhibited concanavalin A stimulated glucose uptake (P less than 0.025 & less than 0.005). Prior incubation with 10(-7) M dexamethasone also significantly inhibited concanavalin A stimulated glucose uptake (P less than 0.005). The known effects of corticosteroids on sphingolipid synthesis, degradation, and tissue levels, suggest inhibition by corticosteroids of glucose uptake may be through effects of the steroid on sphingolipid metabolism.

Dexamethasone inhibition of cholesterol-stimulated glucose transport in 3T3-L1 cells

This study investigates the effects of dexamethasone on cholesterol-stimulated glucose uptake in confluent 3T3-L1 fibroblasts. Dexamethasone pretreatment blocked both insulin-stimulated glucose transport, and the increase produced by exogenous free cholesterol. The dexamethasone effect was inhibited in both cases by cycloheximide. Concentrations of cholesterol which increased glucose transport failed to produce a significant increase in measurable free cholesterol content in the plasma membrane.

Changes in 2-aminoisobutyric acid and cycloleucine uptake produced by 2,4-dichlorophenoxyacetic acid in Chinese hamster ovary cells

The effect of dichlorophenoxyacetic acid on the transport of two non-metabolizable amino acids, 2-aminoisobutyric acid (AIB) and cycloleucine (CL) was studied in chinese hamster ovary (CHO) cells. The herbicide did not exert any direct effect on the AIB transport. However, when the pesticide was in contact with the cells for 24 h an inhibition of the uptake was observed. Removal of the pesticide from the culture medium restored the influx of the amino acids which reached maximum values 1 h before cell division. The transport kinetics showed changes in Vmax but no variations in Km. These results may indicate that 2,4-dichlorophenoxyacetic acid produces a decrease in the carrier number but without modification of the affinity.

Density-dependent regulation of cell growth: an example of a cell-cell recognition phenomenon

Cell-to-cell contact can result in a variety of changes in the cell's physiology. For different cell types, this may include both the initiation as well as the cessation of cell growth and changes in the state of differentiation. This review examines in detail one such phenomenon, density-dependent inhibition of growth, which is observed with many fibroblasts in culture. Data are summarized which demonstrate that the cessation of growth at high cell density is in part a consequence of cell-to-cell contact. An approach to the study of the molecular basis of this phenomenon is presented based on the demonstration that plasma membranes, when bound to sparse growing cells, mimic contact inhibition of growth. The present status of attempts to purify plasma membrane proteins responsible for this effect are summarized, and the properties of these membrane proteins are compared to those of previously described "soluble" proteins that inhibit cellular growth.

Growth inhibitory protein(s) in the 3T3 cell plasma membrane. Partial purification and dissociation of growth inhibitory events from inhibition of amino acid transport

It has been reported previously that a plasma membrane-enriched fraction from 3T3 cells arrests the growth of sparse 3T3 cells early in the G1 phase of growth (Whittenberger et al., '78, '79). Addition of membranes to sparse 3T3 cells also results in a decrease of the rate of transport of alpha-aminoisobutyric acid (Lieberman et al., '79). We have partially purified the growth-inhibitory proteins from plasma membrane of 3T3 cells. These growth-inhibitory proteins behave as intrinsic membrane proteins and do not require membrane lipids for activity. The partially purified proteins arrest cell growth without affecting the rate of alpha-aminoisobutyric transport; thus, inhibition of both transport and cell growth are not obligatorily coupled events.

Effect of 2-hexadecynoic acid on cultured 7288C hepatoma cells

The effects of 2-hexadecynoic acid on the growth and lipid metabolism of cultured 7288 (HTC) cells have been evaluated. Growth was inhibited by the acetylenic acid: the LD50 was 35-85 microM as determined by two methods at low and high cell densities. Reduced growth did not result from damaged plasma membranes as determined by alpha-amino isobutyrate leakage. DNA synthesis was unaffected by the acetylenic acid and the effect on RNA and protein synthesis appeared to be secondary to the effects on lipid metabolism. The 2-hexadecynoic acid inhibited lipid metabolism of the HTC cells at least at two levels. Data from both mass studies and radioactive acetate distributions in cellular and media lipids indicated that fatty acid elongation and acylation, especially triglyceride synthesis, were inhibited.

Growth control by cell to cell contact

Control of cell growth by cell to cell contact is reviewed with particular emphasis on two systems--contact inhibition of growth observed with Swiss 3T3 cells and the mitogenic stimulation of Schwann cells by dorsal root ganglia neurites. In both cases the biological effect can be reproduced by the addition of surface membranes to the corresponding cells. In the case of contact inhibition of 3T3 cells, biological activity appears to correlate with membrane binding to the cells. An octylglucoside extract of 3T3 plasma membranes retains the biological activity (growth inhibition) of the original membranes.